Sudden death, as it is associated with coronary heart disease, is nearly always the result of ventricular fibrillation. The continuing objective of our research effort is to contribute to the development of a standby automatic implanted defibrillation system which will be suitable for use in patients who are at high risk of having out-of-hospital episodes of ventricular fibrillation. In the immediate future, we plan to: 1) try to identify a suitable model for long-term evaluation of implanted defibrillation systems - with particular focus upon the possibility of using very large dogs, 2) refine our microprocessor-based system and use it to critically evaluate several strategies for detecting ventricular fibrillation, and 3) implant a complete defibrillation system in a suitable model for long-term evaluation.